1. Field of the Invention
This invention relates to the preparation of a surface treated carbon black and the compounds derived therefrom. The invention relates to the preparation of a surface treated carbon black which has inherently improved dispersability characteristics and provides rubber compounds with improved dynamic mechanical properties.
2. Discussion of the Prior Art
Improvements in manufacturing of carbon black have allowed for the production of very high surface area carbon black suitable to provide high reinforcement and high levels of wear resistance. With the reduction in the particle size and carbon black structure (the degree of branched connectivity of the carbon black), carbon black becomes increasingly difficult to disperse.
Another phenomenon, carbon black networking, also known as the Payne effect, becomes increasingly prevalent as carbon black content in a rubber compound increases, especially as the particle size decreases and structure increases. This carbon black networking effect is manifested by a dramatic drop in modulus as a function of strain in the rubber compound. This drop in modulus is attributed to a disruption in the carbon black network and is a non-elastic phenomenon. That is to say that the energy required to disrupt this carbon black network is consumed in the disruption of the carbon black aggregate-aggregate interaction and is not recoverable as elastic energy.
The loss in energy due to the Payne effect results in compounds with inherently high loss moduli and, consequently, quite hysteretic. This hysteresis contributes to rolling resistance in pneumatic tire tread compounds increasing fuel consumption.
Previous inventions (Japanese Patent No. 5643/1970, No. 24462/1983, and No. 30417/1968) disclose surface treated carbon black which provide lower cohesive energy density between the particles. However, these materials are not effective in high surface area carbon black. Other patents (U.S. Pat. No. 4,557,306) teach that carbon black modified with Furazan oxides and furazan ring containing compounds provide for improvements in rubber to filler interaction but do not contribute to improvements in the dispersability of the carbon black. And finally, U.S. Pat. No. 4,764,547, teaches that compounds with lower viscosity (thus improved processability) and improved reinforcement properties can be achieved through the use of high surface area carbon black treated with certain amine compounds or quinoline compounds.
Other carbon black coupling agents are known in the art. See, for example T. Yamaguchi et al. in Kautschuk Gummi Kunststoffe, Vol. 42, No. 5, 1989, pages 403-409, which describes a coagent called Sumifine(copyright) (i.e. N,Nxe2x80x2-bis(2-methyl-2-nitropropyl)-1,6-diaminohexane), and L. Gonz{acute over (a )}lez et al. in Rubber Chemistry and Technology, Vol. 69, 1996, pages 266-272. These agents are not used in common practice.
U.S. Pat. No. 4,764,547 teaches that carbon black treated with conventional antidegradants used in the tire industry can afford an improvement in mixing efficiency. These antidegradants are divided into substituted amines such as paraphenylene diamine and quinoline. Both classes of antidegradants are known as primary antidegradants and function by donating a hydrogen atom to a radical.
The use of an amine compound for carbon surface modification is also disclosed in Japanese abstract J6 2250-073-A.
Carbon black can be difficult to disperse in polymers when the surface area is high. The rate of dispersion of carbon black in polymers is proportional to the viscosity of the polymer, that is, a high viscosity polymer provides faster rates of carbon black dispersion. In the cases of isoprene based rubbers and natural rubber, long mixing time increases the amount of heat generated in the compound and thus reduces viscosity and thus the rate and extent of carbon black dispersion. One technique to overcome this difficulty is to mix carbon black into the polymer several times in internal mixers for short intervals each time. This provides for less time for heat to be generated in the mixer and thus the amount of viscosity reduction is minimized and dispersion is improved, but increasing the number of mixing steps also increases the complexity, time required and expense of the process.
In its primary embodiments, the present invention provides compositions comprising a combination of carbon black and at least one surface treating agent selected from the group consisting of quinone compounds, quinoneimine compounds and quinonediimine compounds.
In its second embodiments, the present invention comprises the methods of combining the surface treating agent with the carbon black.
Third embodiments of the present invention relate to compositions resulting from the addition of the above combination of carbon black and one or more surface treating agents to natural or synthetic polymers.
In its fourth embodiments, the present invention relates to methods of dispersing carbon black in a natural or synthetic polymer composition, to achieve increased dispersibility, improved mixing efficiency and improved processability of the composition, comprising treating the surface of carbon black with at least one surface treating agent selected from the group consisting of quinone compounds, quinoneimine compounds and quinonediimine compounds, or mixtures thereof, and mixing the treated carbon black with the polymer composition.
Other embodiments of the invention encompass details about relative amounts of reactants, surface treating agents, carbon black, rubber compositions and methods of combining carbon black and surface treating agents and dispersing the carbon black into the polymer composition all of which are hereinafter disclosed in the following discussion of each of the facets of the invention.